How evolution contributed to the demise of the passenger pigeon

Passenger pigeons were once the most abundant bird in North America, and quite possibly the world.

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In a matter of decades, the continent’s most common bird has been completely wiped out, down to the last individual. “It’s always astounded me how something could have that large a population and entirely disappear,” says Beth Shapiro from the University of California, Santa Cruz. “Why didn’t tiny populations survive somewhere in refugia? I mean, we are pretty good at murdering things, but how did we kill every one of them?”

[W]hy did this superspecies die out? Shapiro thinks it’s because the bird specifically evolved to live in mega-flocks, and developed adaptations that became costly when their numbers suddenly shrank at human hands.

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The fact is that “human persecution was relentless right up until the very end,” [researcher Ben Novak] says. “The rarer the birds became, harvesting efforts only grew more intense. Whatever maladaptive trade-offs may have existed for the passenger pigeon, their decline was simply too rapid for these trade-offs to show symptoms.”